This invention concerns a two-stroke motorcycle lubricant.
The function of a lubricant in a two-stroke motorcycle engine is to lubricate and cool moving parts. In a two-stroke motorcycle engine lubricant is burnt along with a fuel charge, which leaves deposits of burnt products in the exhaust, the exhaust port, the combustion chamber and on the piston. These deposits lead to a decrease in the engine performance and they reduce the total working life of the engine, and the exhaust.
Modern two-stroke lubricants usually comprise a balance of additives in a base oil, with a thickener and solvent.
The additives are normally detergents, dispersants and antioxidants. The detergents are oil soluble metallic soaps such as sulphonates or phenates. An example of a detergent that could be used is Hitec 614, which is available from The Ethyl Corporation. Fully formulated additive packages such as Lubrizol 600, which is available from The Lubrizol Corporation, are also used. Lubrizol 600 contains a phenate soap detergent and a succinimide dispersant. The detergents or formulated additive packages are added to lubricants to minimise the build up of deposits.
The base oils are carriers for the additives and they aid in the load carrying capability of the lubricant. The base oils are normally mineral based having a pour point of greater than -12.degree. C. A lubricant cannot just comprise a mineral base oil and additives because it would not pass the JASO smoke test FC level (see later for details of the test). In order to pass the JASO smoke test FC level, a polyisobutene (PIB) thickener is added. Polyisobutene has a very low smoke level relative to mineral oil which enables the lubricant to pass the test. The PIB is usually required in a concentration of greater than 20%. Finally, if a high viscosity base oil is used in the lubricant, a hydrocarbon solvent, such as white spirit, is required to aid miscibility with the fuel. Typically the concentration of the solvent is around 20%.
Current lubricants have disadvantages that can affect the longevity of the engine. Normal detergent additive chemistries are ash-containing, i.e. they are based on metallic sulphonate or phenate soaps, which can lead to increased deposit formation in the combustion chamber and spark plug whiskering, i.e. a build-up of metallic salts or "ash" on the spark plug electrode. These effects can lead to starting problems, reduced performance and possible engine damage.
The mineral base oils that are routinely chosen for two-stroke lubricants lead to deposits (i.e. decomposition products) that can block the exhaust port and progressively clog the exhaust. This leads to reduced top speed and increased fuel consumption, giving poor combustion and increased emissions.
The lubricity or load carrying capability of two-stroke lubricants is generally acceptable and seizures are uncommon. However, the adequate lubricity of the lubricant is often offset by relatively poor detergency. A good two-stroke lubricant needs all round performance.
These effects described above can occur in less than 5000 km, causing decreased engine performance and possibly even causing damage to the motorcycle engine.
A further disadvantage for the lubricant manufacturer is the dark colour of finished two-stroke lubricants comprising mineral base oils and metallic soap detergents. Dark coloured lubricants may be perceived by the consumer to be of a lower quality or to contain used oils. It is difficult for the manufacturer to dye dark oils.
The aim of the present invention is to provide further detergents and base oils for a two-stroke motorcycle lubricant.
It is a further aim of the present invention to provide a detergent that will not block exhausts and catalysts, and will maintain excellent levels of cleanliness and very low levels of exhaust smoke, whilst maintaining high load carrying capacity.
In accordance with the present invention there is provided a two-stroke motorcycle lubricant comprising a base oil having a viscosity at 100.degree. C. of less than 8 cSt and a pour point below -30.degree. C., preferably below -39.degree. C.
In accordance with the present invention there is also provided use of an ashless, oil-soluble amine as a detergent in a two-stroke motorcycle lubricant.
The oil-soluble amine is referred to as an ashless, oil-soluble amine because it does not contain any metallic functionality.
The viscosity of the base oil at 100.degree. C. is preferably below 6 cSt, more preferably below 4 cSt, and even more preferably around 2 cSt. The base oil is preferably a mineral oil derived from a naphthenic crude source or a polyalphaolefin.
The ashless, oil-soluble amine preferably has a molecular weight of at least 450, more preferably in the range 900-1500. The ashless, oil-soluble amine is preferably: a polyisobutene-amine; a polyisobutene-phenolamine; a polyetheramine; or a combination thereof.
The inventor has found that if he uses a detergent comprising an ashiess, oil-soluble amine in combination with base oils having low viscosity (i.e. less than 8 cSt at 100.degree. C.) and low pour point (i.e. below -30.degree. C.) in a two-stroke motorcycle lubricant, the two-stroke motorcycle lubricant exhibits excellent detergency, there is a reduction in the blocking of exhausts and catalysts, and very low levels of smoke are produced. Furthermore, the lubricants are extremely light in colour, they are attractive to the consumer, and they are capable of being dyed different colours by the manufacturer.
The two-stroke motorcycle lubricant may also include a thickener. The thickener is preferably a polyisobutene, preferably having a molecular weight of greater than 450, more preferably greater than 950. The thickener is more preferably a reactive polyisobutene, preferably having a molecular weight of greater than 450, more preferably greater than 950. A reactive polyisobutene differs from a standard polyisobutene in that at least 80% of the terminal unsaturation is in the alpha position. Suitable conventional polyisobutenes are Hyvis 07 and Hyvis 10, and suitable reactive polyisobutenes are Ultravis 5 and Ultravis 10, all of which are available from BP Chemicals. The polyisobutene thickener is added to the two-stroke lubricant to increase the viscosity without having a detrimental effect on smoke and deposit formation. High viscosity mineral base oils may be used to increase a lubricant's viscosity, but they have a negative effect on smoke and deposit formation.